In charged particle systems, comprising both electron microscopes and focused ion beam systems, a column is typically used to focus a charged particle beam onto the surface of a target to be imaged and (optionally) processed using the beam. In these columns, a charged particle source generates the initial beam of electrons or ions, which then passes into a charged particle “gun”, which typically focuses the charged particles into a roughly parallel beam which enters the main body of the column where this beam may be blanked (i.e., turned on and off), deflected (moved around on the target surface), and focused onto the surface of the target. The component within the source from which the charged particles originate is termed the “emitter”, typically comprising a very sharp metal point. Generally, in the prior art, the charged source has comprised a single charged particle emitter, such as a cold-field emitter or Schottky emitter for electrons, or a gaseous field ionization or liquid metal ion source for ions (normally positively charged). In the case of liquid metal ion sources (LMIS), this metal point is a liquid, but in other source types, the metal is a solid, often called a “tip”. Carbon nanotubes can also be used as electron emitters. In all cases, however, these emitters are characterized by a finite lifetime, limited by various factors such as surface contamination, or ion bombardment erosion of the tip, causing it to become blunter over time until emission is no longer sustainable at acceptable extraction voltages.
For optimized operation of the charged particle column, it is necessary for the source to be precisely aligned to the symmetry (or optical) axis of the column, typically to within 5 to 20 μm. Thus, charged particle sources are generally supported by multi-axis motion assemblies allowing source motion during system operation. The image formed by the column on a target is observed, and the source is then moved until the image is has sufficient contrast and resolution for the particular application required. In some cases, the charged particle beam may be used for processing of the target, in addition to imaging, such as electron beam induced etching (EBIE), electron beam induced deposition (EBID), ion milling, ion beam induced etching (IBIE), ion beam induced deposition (IBID), secondary ion mass spectrometry (SIMS), etc.